Atom‐Precise Organometallic Zinc Clusters

The bottom‐up synthesis of organometallic zinc clusters is described. The cation {[Zn₁₀](Cp*)₆Me}⁺ ( 1 ) is obtained by reacting [Zn₂Cp*₂] with [FeCp₂][BAr₄^F] in the presence of ZnMe₂. In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower‐nuclearity clusters {[Zn₉](Cp*)₆} ( 2 ) and {[Zn₈](Cp*)₅(^tBuNC)₃}⁺ ( 3 ). According to DFT calculations, 1 and 2 can be described as closed‐shell species that are electron‐deficient in terms of the Wade–Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal–metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements).     

Phosphoramidate‐Supported Cp*IrIII Aminoborane H2B=NR2 Complexes: Synthesis,Structure, and Solution Dynamics

Reaction of aminoboranes H₂B=NR₂ (R=iPr or Cy) with the cationic Cp*Ir^III phosphoramidate complex [IrCp*{κ²‐N,O‐Xyl(N)P(O)(OEt)₂}][BAr^F₄] generates the aminoborane complexes [IrCp*(H){κ¹‐N‐η²‐HB‐Xyl(N)P(OBHNR₂)(OEt)₂}][BAr^F₄] (R=iPr or Cy) in which coordination of a P=O bond with boron weakens the B=N multiple bond. For these complexes, solution‐ and solid‐state, as well as DFT computational techniques, have been employed to substantiate B?N bond rotation of the coordinated aminoborane.     

Isolation and Structure of Germylene‐Germyliumylidenes Stabilized by N‐Heterocyclic Imines

The ditopic germanium complex FGe(NIPr)₂Ge[BF₄] ( 3 [BF₄]; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) is prepared by the reaction of the amino(imino)germylene (Me₃Si)₂NGeNIPr ( 1 ) with BF₃?OEt₂. This monocation is converted into the germylene‐germyliumylidene 3 [BAr^F₄] [Ar^F=3,5‐(CF₃)₂‐C₆H₃] by treatment with Na[BAr^F₄]. The tetrafluoroborate salt 3 [BF₄] reacts with 2 equivalents of Me₃SiOTf to give the novel complex (OTf)(GeNIPr)₂[OTf] ( 4 [OTf]), which affords 4 [BAr^F₄] and 4 [Al(OR^F)₄] [R^F=C(CF₃)₃] after anion exchange with Na[BAr^F₄] or Ag[Al(OR^F)₄], respectively. The computational, as well as crystallographic study, reveals that 4 ⁺ has significant bis(germyliumylidene) dication character.     

Facile access to the pnictocenium ions [Cp*ECl]+ (E = P, As) and [(Cp*)2P]+: chloride ion affinity of Al(OR(F))3

The pnictocenium salts [Cp*PCl]⁺[μCl]^? ( 1 a ), [Cp*PCl]⁺[ClAl(OR^F)₃]^? ( 1 b ), [Cp*AsCl]⁺[ClAl(OR^F)₃]^? ( 2 ), and [(Cp*)₂P]⁺[μCl]^? ( 3 ), in which Cp*=Me₅C₅, μCl=(^FRO)₃Al? Cl? Al(OR^F)₃, and OR^F=OC(CF₃)₃, were prepared by halide abstraction from the respective halopnictines with the Lewis superacid PhF→Al(OR^F)₃. 1 The X‐ray crystal structures of 1 a , 2 , and 3 established that in the half as well as in the sandwich cations the Cp* rings are attached in an η²‐fashion. By using one or two equivalents of the Lewis acid, the two new weakly coordinating anions [μCl]^? and [ClAl(OR^F)₃]^? resulted. They also stabilize the highly reactive cations in PhF or 1,2‐F₂C₆H₄ solution at room temperature. The chloride ion affinities (CIAs) of a range of classical strong Lewis acids were also investigated. The calculations are based on a set of isodesmic BP86/SV(P) reactions and a non‐isodesmic reference reaction assessed at the G3MP2 level.     

Ethyl‐Zinc(II)‐Cation Equivalents: Synthesis and Hydroamination Catalysis

Ion‐like ethylzinc(II) compounds with weakly coordinating aluminates [Al(OR^F)₄]^? and [(R^FO)₃Al‐F‐Al(OR^F)₃]^? (R^F=C(CF₃)₃) were synthesized in a one‐pot reaction and fully characterized by single‐crystal X‐ray diffraction, NMR and vibrational spectroscopy, and by quantum chemical calculations. The catalytic activity of ion‐like Et‐Zn[Al(OR^F)₄] in intermolecular hydroamination and in the unusual double hydroamination of anilines and alkynes was investigated. Favorable performance was also found in comparison to the Et₂Zn/ [PhNMe₂H]⁺[B(C₆F₅)₄]^? system generated in situ at lower catalyst loadings of 2.5 mol %.     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

Ruthenium bidentate phosphine complexes for the coordination and catalytic dehydrogenation of amine- and phosphine-boranes

Addition of the amine–boranes H₃B ? NH₂tBu, H₃B ? NHMe₂ and H₃B ? NH₃ to the cationic ruthenium fragment [Ru(xantphos)(PPh₃)(OH₂)H][BAr^F₄] ( 2 ; xantphos=4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; BAr^F₄=[B{3,5‐(CF₃)₂C₆H₃}₄]^?) affords the η¹‐B? H bound amine–borane complexes [Ru(xantphos)(PPh₃)(H₃B ? NH₂tBu)H][BAr^F₄] ( 5 ), [Ru(xantphos)(PPh₃)(H₃B ? NHMe₂)H][BAr^F₄] ( 6 ) and [Ru(xantphos)(PPh₃)(H₃B ? NH₃)H][BAr^F₄] ( 7 ). The X‐ray crystal structures of 5 and 7 have been determined with [BAr^F₄] and [BPh₄] anions, respectively. Treatment of 2 with H₃B ? PHPh₂ resulted in quite different behaviour, with cleavage of the B? P interaction taking place to generate the structurally characterised bis‐secondary phosphine complex [Ru(xantphos)(PHPh₂)₂H][BPh₄] ( 9 ). The xantphos complexes 2 , 5 and 9 proved to be poor precursors for the catalytic dehydrogenation of H₃B ? NHMe₂. While the dppf species (dppf=1,1′‐bis(diphenylphosphino)ferrocene) [Ru(dppf)(PPh₃)HCl] ( 3 ) and [Ru(dppf)(η⁶‐C₆H₅PPh₂)H][BAr^F₄] ( 4 ) showed better, but still moderate activity, the agostic‐stabilised N‐heterocyclic carbene derivative [Ru(dppf)(ICy)HCl] ( 12 ; ICy=1,3‐dicyclohexylimidazol‐2‐ylidene) proved to be the most efficient catalyst with a turnover number of 76 h^?1 at room temperature.     

Insertion Reactions of Heterocumulenes with Zincocene Cp*2Zn

Zincocene Cp*₂Zn reacts with carbodiimides C(NR)₂ with insertion into the Zn–Cp* bond and formation of [(Cp*C(NR)₂]₂Zn [R = Et ( 1 ), iPr ( 2 ), Cy ( 3 )]. In addition, the reaction of Cp*₂Zn with CS₂ under dry conditions gives (Cp*CS₂)₂Zn ( 4 ), whereas in the presence of a small amount of water [Zn₄(μ₄‐O)(S₂CCp*)₆] ( 5 ) is obtained. Compounds 1 – 4 were characterized by NMR (¹H, ¹³C) and IR spectroscopy as well as elemental analysis and single‐crystal X‐ray diffraction ( 2 – 4 , 5 of poor quality). The solid‐state structure of 5 is comparable to the carboxylate complex previously obtained from the reaction of Cp*₂Zn with CO₂.     

1,3-Diene Polymerization Promoted by Half-Sandwich Rare-Earth-Metal Dimethyl Complexes: Active Species Clustering and Cationization/Deactivation Processes

When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe₂]₃ (Ln=Y, Lu; Cp*=C₅Me₅) promote efficiently the formation of high-cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl. ¹H DOSY). The occurrence of donor-solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe₂]₃ and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*₃Y₃Me₄(CH₂)(thf)₂] and [Cp*₆Y₆Me₄(CH₂)₄], as well as [(Cp*Y)₂Me₂(N(Me)₂(C₆H₄)]_n[B(C₆F₅)₄]_n, implying a multimetallic active species.     

Half‐Sandwich Iridium Complexes Bearing a Diprotic Glyoxime Ligand: Structural Diversity Induced by Reversible Deprotonation

Synthesis and deprotonation reactions of half‐sandwich iridium complexes bearing a vicinal dioxime ligand were studied. Treatment of [{Cp*IrCl(μ‐Cl)}₂] (Cp*=η⁵‐C₅Me₅) with dimethylglyoxime (LH₂) at an Ir:LH₂ ratio of 1:1 afforded the cationic dioxime iridium complex [Cp*IrCl(LH₂)]Cl ( 1 ). The chlorido complex 1 undergoes stepwise and reversible deprotonation with potassium carbonate to give the oxime–oximato complex [Cp*IrCl(LH)] ( 2 ) and the anionic dioximato(2?) complex K[Cp*IrCl(L)] ( 3 ) sequentially. Meanwhile, twofold deprotonation of the sulfato complex [Cp*Ir(SO₄)(LH₂)] ( 4 ) resulted in the formation of the oximato‐bridged dinuclear complex [{Cp*Ir(μ‐L)}₂] ( 5 ). X‐ray analyses disclosed their supramolecular structures with one‐dimensional infinite chain ( 1 and 2 ), hexagonal open channels ( 3 ), and a tetrameric rhomboid ( 4 ) featuring multiple intermolecular hydrogen bonds and electrostatic interactions.     

Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu3)2]+ with Aryl Bromides: Aryl?Br and Phosphine Ligand C?H Activation

Oxidative addition of aryl bromides to 12‐electron [Rh(PiBu₃)₂][BAr^F₄] (Ar^F=3,5‐(CF₃)₂C₆H₃) forms a variety of products. With p‐tolyl bromides, Rh^III dimeric complexes result [Rh(PiBu₃)₂(o/p‐MeC₆H₄)(μ‐Br)]₂[BAr^F₄]₂. Similarly, reaction with p‐ClC₆H₄Br gives [Rh(PiBu₃)₂(p‐ClC₆H₄)(μ‐Br)]₂[BAr^F₄]₂. In contrast, the use of o‐BrC₆H₄Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C? H activation: [Rh{PiBu₂(CH₂CHCH₃C H₂)}(PiBu₃)(μ‐Br)]₂[BAr^F₄]₂. Trapping experiments with ortho‐bromo anisole or ortho‐bromo thioanisole indicate that a possible intermediate for this process is a low‐coordinate Rh^III complex that then undergoes C? H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rh(PiBu₃)₂(C₆H₄O Me)Br][BAr^F₄] (the solid‐state structure of the 5‐methyl substituted analogue is reported) and [Rh(PiBu₃)₂(C₆H₄S Me)Br][BAr^F₄]. The anisole‐derived complex proceeds to give [Rh{PiBu₂(CH₂CHCH₃C H₂)}(PiBu₃)(μ‐Br)]₂[BAr^F₄]₂, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu₃)₂(C₆H₄O Me)Br][BAr^F₄] and its onward reactivity to give the products of C? H activation and aryl elimination suggest that it is implicated on the pathway of a σ‐bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C? H bond cleavage through phosphine‐assisted deprotonation of a non‐agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C? H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid‐state by X‐ray crystallography.     

The Influence of N‐Heterocyclic Carbenes (NHC) on the Reactivity of [Ru(NHC)4H]+ With H2, N2, CO and O2

The five‐coordinate ruthenium N‐heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr₂Me₂)₄H][BAr^F₄] ( 1 ; IiPr₂Me₂=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene; Ar^F=3,5‐(CF₃)₂C₆H₃), [Ru(IEt₂Me₂)₄H][BAr^F₄] ( 2 ; IEt₂Me₂=1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene) and [Ru(IMe₄)₄H][BAr^F₄] ( 3 ; IMe₄=1,3,4,5‐tetramethylimidazol‐2‐ylidene) have been synthesised following reaction of [Ru(PPh₃)₃HCl] with 4–8 equivalents of the free carbenes at ambient temperature. Complexes 1 – 3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about δ ?41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe₄)₄(MeCN)H][BAr^F₄], 4 . The reactivity of 1 – 3 towards H₂ and N₂ depends on the size of the N‐substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H₂ and N₂ only at low temperature and incompletely, while 3 affords [Ru(IMe₄)₄(η²‐H₂)H][BAr^F₄] ( 7 ) and [Ru(IMe₄)₄(N₂)H][BAr^F₄] ( 8 ) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1 – 3 to give [Ru(NHC)₄(CO)H][BAr^F₄] ( 9 – 11 ). Addition of O₂ to solutions of 2 and 3 leads to rapid oxidation, from which the Ru^III species [Ru(NHC)₄(OH)₂][BAr^F₄] and the Ru^IV oxo chlorido complex [Ru(IEt₂Me₂)₄(O)Cl][BAr^F₄] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO ? O₂ > N₂ > H₂.     

Improving the Performance of Heterogeneous Borane Cocatalysts by Pretreatment of the Silica Support with Alkylaluminum Compounds

The treatment of silica with alkylaluminum compounds, triisobutylaluminum (TIBA) and triethylaluminum (TEA), dramatically enhanced the cocatalytic performances of the [CPh₃]⁺[B(C₆F₅)₃—SiO₂]^–. We measured the productivity and ethylene‐consumption profiles for [CPh₃]⁺[B(C₆F₅)₃—SiO₂]^– cocatalysts and Cp₂ZrCl₂/TIBA. Both of the treated cocatalyst systems improved the average molecular weight of the product when compared with the untreated cocatalyst system. The TIBA‐treated cocatalyst provided a narrow molecular weight distribution while the TEA‐treated cocatalyst system gave a broad distribution.     

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

Chloride abstraction from [(R,R)‐(^iPrDuPhos)Co(μ‐Cl)]₂ with NaBAr^F₄ (BAr^F₄=B[(3,5‐(CF₃)₂)C₆H₃]₄) in the presence of dienes, such as 1,5‐cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought‐after cationic bis(phosphine) cobalt complexes, [(R,R)‐(^iPrDuPhos)Co(η²,η²‐diene)][BAr^F₄]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18‐electron, cationic cobalt(I) arene complexes, as well as the [(R,R)‐(^iPrDuPhos)Co(diene)][BAr^F₄] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [(R,R)‐(^iPrDuPhos)Co(MAA)][BAr^F₄] (MAA=methyl 2‐acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin–Hammett kinetic regime similar to rhodium catalysis.     

[PdCl(TeMe2)3](BArF) – The First Structurally Characterized Palladium(II) Complex with TeMe2 Ligands

[PdCl(TeMe₂)₃]BAr^F ( 4 ) forms as the major tellurium containing product from the reaction of [(4‐Mebti)PdCl] with TeMe₂ and Na(BAr^F) and is isolated by crystallization from the reaction mixture. At ?20 °C, the compound forms orange columns from toluene/pentane, space group , with Z = 2. In the solid, the cationic [PdCl(TeMe₂)₃]⁺ complex ions show a non‐planar PdClTe₃ coordination unit and are associated to dimers via weak Pd···Te interactions.     

Halfsandwich Complexes Containing the Tetrathiotungstate Chelate Ligand. Crystal and Molecular Structure of Cp*Rh(PMe3)[(μ‐S)2WS2] (Cp* = η5‐Pentamethylcyclopentadienyl)

The reactions of Cp*M(PMe₃)Cl₂ (M = Rh ( 1a ), Ir ( 1b )) with (NEt₄)₂[WS₄] led to the heterodimetallic sulfido‐bridged complexes Cp*M(PMe₃)[(μ‐S)₂WS₂] (M = Rh ( 2a ), Ir ( 2b )), whereas the dimers [Cp*MCl(μ‐Cl)]₂ (M = Rh ( 4a ), Ir ( 4b )) reacted with (NEt₄)₂[WS₄) to give the known trinuclear compounds [Cp*M(Cl)]₂(μ‐WS₄) (M = Rh ( 5a ), Ir ( 5b )). Hydrolysis of the terminal W=S bonds converts 2a, b into Cp*M(PMe₃)[(μ‐S)₂WO₂] (M = Rh ( 3a ), Ir ( 3b )). Salts of a heterodimetallic anion, A[CpMo(I)(NO)(WS₄)] ( 6 ) (A⁺ = NEt₄⁺, NPh₄⁺) were obtained by reactions of [CpMo(NO)I₂]₂ with tetrathiotungstates, A₂[WS₄]. The complexes were characterized by IR and NMR (¹H, ¹³C, ³¹P) spectroscopy, and the X‐ray crystallographic structure of Cp*Rh(PMe₃)[(μ‐S)₂WS₂] ( 2a ) has been determined. The bond lengths and angles in the coordinations spheres of Rh and W in 2a (Rh···W 288.5(1) pm) are compared with related complexes containing terminal [WS₄^2—] chelate ligands.     

Synthesis and Application of a Perfluorinated Ammoniumyl Radical Cation as a Very Strong Deelectronator

The perfluorinated dihydrophenazine derivative (perfluoro‐5,10‐bis(perfluorophenyl)‐5,10‐dihydrophenazine) (“phenazine^F”) can be easily transformed to a stable and weighable radical cation salt by deelectronation (i.e. oxidation) with Ag[Al(OR^F)₄]/ Br₂ mixtures (R^F=C(CF₃)₃). As an innocent deelectronator it has a strong and fully reversible half‐wave potential versus Fc⁺/Fc in the coordinating solvent MeCN (E°′=1.21 V), but also in almost non‐coordinating oDFB (=1,2‐F₂C₆H₄; E°′=1.29 V). It allows for the deelectronation of [Fe^IIICp*₂]⁺ to [Fe^IV(CO)Cp*₂]²⁺ and [Fe^IV(CN‐^tBu)Cp*₂]²⁺ in common laboratory solvents and is compatible with good σ‐donor ligands, such as L=trispyrazolylmethane, to generate novel [M(L)_x]ⁿ⁺ complex salts from the respective elemental metals.     

Construction of tetranuclear macrocycles through C-H activation and structural transformation induced by [2+2] photocycloaddition reaction

A series of binuclear complexes [{Cp*Ir(OOCCH₂COO)}₂(pyrazine)] ( 1 b ), [{Cp*Ir(OOCCH₂COO)}₂(bpy)] ( 2 b ; bpy=4,4′‐bipyridine), [{Cp*Ir(OOCCH₂COO)}₂(bpe)] ( 3 b ; bpe=trans‐1,2‐bis(4‐pyridyl)ethylene) and tetranuclear metallamacrocycles [{(Cp*Ir)₂(OOC‐C?C‐COO)(pyrazine)}₂] ( 1 c ), [{(Cp*Ir)₂(OOC‐C?C‐COO)(bpy)}₂] ( 2 c ), [{(Cp*Ir)₂(OOC‐C?C‐COO)(bpe)}₂] ( 3 c ), and [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](pyrazine)}₂] ( 1 d ), [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](bpy)}₂] ( 2 d ), [{(Cp*Ir)₂[OOC(H₃C₆)‐N?N‐(C₆H₃)COO](bpe)}₂] ( 3 d ) were formed by reactions of 1 a – 3 a {[(Cp*Ir)₂(pyrazine)Cl₂] ( 1 a ), [(Cp*Ir)₂(bpy)Cl₂] ( 2 a ), and [(Cp*Ir)₂(bpe)Cl₂] ( 3 a )} with malonic acid, fumaric acid, or H₂ADB (azobenzene‐4,4′‐chcarboxylic acid), respectively, under mild conditions. The metallamacrocycles were directly self‐assembled by activation of C? H bonds from dicarboxylic acids. Interestingly, after exposure to UV/Vis light, 3 c was converted to [2+2] cycloaddition complex 4 . The molecular structures of 2 b , 1 c , 1 d , and 4 were characterized by single‐crystal x‐ray crystallography. Nanosized tubular channels, which may play important roles for their stability, were also observed in 1 c , 1 d , and 4 . All complexes were well characterized by ¹H NMR and IR spectroscopy, as well as elemental analysis.     

Speciation of [Cp*2M2O5] in Polar and Donor Solvents

The speciation of compounds [Cp*₂M₂O₅] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by ¹H NMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)‐assisted ionic dissociation to generate [Cp*MO₂(S)]⁺ and [Cp*MO₃]^? takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO₂(OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN≈acetone<MeOH<DMSO. Addition of a base (Et₃N) converts [Cp*₂M₂O₅] into [Et₃NH]⁺[Cp*MO₃]^?, for which the presence of a N? H???O?M interaction is revealed by ¹H NMR spectroscopy in comparison with the sodium salts, Na⁺[Cp*MO₃]^?. These are fully dissociated in DMSO and MeOH, but display a slow equilibrium between free ions and the ion pair in MeCN and acetone. Only one resonance is observed for mixtures of [Cp*MO₃]^? and [Cp*MO₂(OH)] because of a rapid self‐exchange. In the presence of extensive ionic dissociation, only one resonance is observed for mixtures of the cationic [Cp*MO₂(S)]⁺ product and the residual undissociated [Cp*₂M₂O₅] because of a rapid associative exchange via the trinuclear [Cp*₃M₃O₇]⁺ intermediate. In neat methanol, complex [Cp*₂W₂O₅] reacts to yield extensive amounts of a new species, formulated as the mononuclear methoxido complex [Cp*WO₂(OMe)] on the basis of the DFT study. An equivalent product is not observed for the Mo system. The addition of increasing amounts of water results in the rapid decrease of this product in favor of [Cp*₂W₂O₅] and [Cp*WO₂(OH)].     

Crystallographic report: The [bis(η5‐methylcyclopentadienyl)titanium(IV)‐bis(N‐methylglycine)] dichloride

The crystal network of [Cp′₂Ti(N?CH₃? Gly)₂]²⁺[Cl^?]₂ (Cp′ = (CH₃)C₅H₄) complex, which crystallizes as a solvate with CH₃OH, is built up with discrete cationic units connected through intermolecular H· · ·Cl bonds. The α‐amino acid ligands are attached through an intramolecular H· · ·O bond within one cationic unit. Copyright © 2004 John Wiley & Sons, Ltd.